In recent years, reduction in size and an increase in capacity of a magnetic recording device such as a hard disk drive (HDD) have been rapidly accelerated. Therefore, recording density is demanded to be higher with an increase in capacity of a magnetic recording medium. In order to make the recording density higher, magnetic particles of the magnetic recording medium are miniaturized (diameter: approximately 8 nm). A perpendicular magnetic recording, i.e., a technology for magnetizing a recording surface in the direction perpendicular to the recording surface is employed for responding to the demand to make the recording density higher.
As a medium for the perpendicular magnetic recording for making the recording density of the magnetic recording medium higher, a discrete track medium (DTM) has been proposed. In the discrete track medium, a nonmagnetic region is formed between adjacent tracks and recording is performed on only the tracks formed of a magnetic material. Furthermore, a bit patterned medium (BPM) has been proposed. In the bit patterned medium, magnetic particles are isolated and a single bit pattern is produced so as to improve recording resolution.
The discrete track medium is patterned into a convex-concavo form radially and the bit patterned medium is patterned into a convex-concavo form both circumferentially and radially. On these media, a pattern having concave portions (non-pattern portions) and convex portions (pattern portions) in accordance with a servo pattern is also formed on a servo region, so that the recording density can be improved.
Here, an outline of the servo region of the patterned medium mentioned above is described. FIG. 11 is a cross-sectional view for explaining an example of a servo pattern on a conventional servo region 20. As illustrated in FIG. 11, the servo region 20 forming a magnetic recording medium has a configuration in which an intermediate layer 10 is laminated on an upper surface of a substrate 9, and a magnetic recording layer 11 on which a convex-concavo pattern is formed is provided on an upper surface of the intermediate layer 10.
As illustrated in FIG. 11, convex-concavo pattern portions are alternately formed on the magnetic recording layer 11. Magnetic recording layers 13 are provided on pattern portions 12 as convex portions and nonmagnetic layers 15 are filled into non-pattern portions 14 as concave portions. Note that information is expressed by presence or absence of magnetization in one direction that is either of an upward direction or a downward direction on the servo pattern. Therefore, as illustrated in FIG. 11, the magnetic recording layers 13 are formed as the magnetic recording layers 13 on which servo signals are magnetized in a predetermined direction (upward direction in FIG. 11).
Furthermore, as a configuration of the servo region of the magnetic recording medium of this type, the following configuration has been disclosed (for example, Patent Literature 1). In this configuration, upper magnetic layers of the concave portions in the convex-concavo pattern forming the servo region are removed, so that a coercive force of the concave portions is increased. The servo region is magnetized in one direction, so that a magnetization direction of the convex portions is inverted. In this manner, with the configuration in which the magnetization direction of the convex portions in the convex-concavo pattern on the servo region is inverted, the servo signals on the servo region can be increased.